I think there is only one "rapture" as we call it. A one time event when those who are alive are caught up and changed. They will not undergo death as we know it. The other events are clearly resurrections of the dead. Those spoken of in revelation 20 are clearly those who will have died as martyrs during the great tribulation on earth. There is considerable debate concerning when this "rapture" event happens. I personally believe it occurs before the 70th week.
I think that the understanding of the "first" resurrection may be what confuses people. I do not necessarily believe that the term "first" necessitates an ordinal value. But rather two varieties of resurrection- one to life and the other to condemnation. The first resurrection is the principal one, the primary one- the one that leads to life eternal. It also happens that this kind of resurrection occurs before the other kind which is the resurrection to judgment that leads to the second death.
Throughout scripture there are two kinds of resurrection spoken of:
46 “These will go away into eternal punishment, but the righteous into eternal life.”
25 “Truly, truly, I say to you, an hour is coming and now is, when the dead will hear the voice of the Son of God, and those who hear will live.
26 “For just as the Father has life in Himself, even so He gave to the Son also to have life in Himself;
27 and He gave Him authority to execute judgment, because He is the Son of Man.
28 “Do not marvel at this; for an hour is coming, in which all who are in the tombs will hear His voice,
29 and will come forth; those who did the good deeds to a resurrection of life, those who committed the evil deeds to a resurrection of judgment.
14 “But this I admit to you, that according to the Way which they call a sect I do serve the God of our fathers, believing everything that is in accordance with the Law and that is written in the Prophets;
15 having a hope in God, which these men cherish themselves, that there shall certainly be a resurrection of both the righteous and the wicked.
Christ was the first to experience the resurrection of the righteous, the two witnesses will also experience this resurrection during the tribulation, the tribulation martyrs will experience this as well as we see in Rev 20. And so will those who are dead in Christ when the rapture happens, they also will experience this kind of resurrection whatever your view on timing is. And again so will those righteous that will be raised at the end of the Millennium, who will have lived and died as mortals on the earth during Christ's 1000 year reign. So you can see there is more than one resurrection of this kind- of the righteous to life. Even if you believe that the righteous are all raised at the end of the tribulation, there is no denying that Christ has already experienced this kind of resurrection so saying that there is only one resurrection for the righteous would be in error because Christ already was the first.
The wicked will be raised at the end of the millennium, that is the only time we see in scripture a resurrection to judgment.
Two kinds of resurrection, not two as in there is only one followed by the last.